In a conventional solid-state imaging device, light-gathering on-chip lenses corresponding to respective pixels are provided on the light receiving surface side of a substrate. Light that is gathered by the on-chip lenses enters the light receiving units of the respective pixels formed in the substrate, and signal charges in accordance with the amounts of light are generated at the light receiving units.
The tilt of a principal ray that enters the solid-state imaging device via an imaging optical system provided in an imaging apparatus or the like becomes greater in the periphery of the pixel region. Therefore, at the pixels in the periphery of the pixel region formed in the solid-state imaging device, light gathered by the corresponding on-chip lenses does not enter the central portions of the light receiving units.
To counter this problem, Patent Document 1 discloses a technique by which the pitch of the on-chip lenses corresponding to the light receiving units of the respective pixels becomes narrower toward the periphery of the pixel region, compared with the pitch of the light receiving units. With this arrangement, shading correction is performed. As the pitch of the on-chip lenses is made to differ between the central region of the pixel region and the periphery of the pixel region, light that enters obliquely can be gathered into the central portion of each light receiving unit in the periphery of the pixel region.
Meanwhile, so as to improve photoelectric conversion efficiency and sensitivity to incident light, a solid-state imaging device of a so-called back-illuminated type has been recently suggested. In a solid-state imaging device of a back-illuminated type, a drive circuit is formed on the surface side of a semiconductor substrate, and the back surface of the semiconductor substrate serves as the light receiving surface. As an interconnect layer is provided on the opposite side of the substrate from the light receiving surface in the solid-state imaging device of the back-illuminated type, the distance between the light receiving units formed in the substrate and the surfaces of the on-chip lenses provided on the light incidence side of the substrate becomes shorter, and accordingly, sensitivity is increased.
Patent Document 2 discloses a solid-state imaging device of a back-illuminated type in which a trench is formed to a predetermined depth from the light receiving surface (back surface) of the substrate so as to reduce color mixing, and photodiode regions are isolated from one another by burying an insulating material in the trench. As the respective photodiode regions are isolated from one another by the insulating material buried in the trench, electrons generated in a photodiode region do not leak into an adjacent photodiode region, and color mixing can be reduced.